An Insight towards Trends and Effectiveness of Vertical ... · An Insight towards Trends and Effectiveness of ... enhanced reception with less probability of call drop and ... analysis

Communications on Applied Electronics (CAE) – ISSN : 2394-4714

Foundation of Computer Science FCS, New York, USA

Volume 4– No.5, February 2016 – www.caeaccess.org

35

An Insight towards Trends and Effectiveness of Vertical

Handoff Mechanism

Hemavathi Research Scholar

Dept. of ECE, BMSCE, Bangalore, India

S. Akhila Prof., Dept. of ECE

BMSCE, Bangalore, India

ABSTRACT

With increasing technological advancement of mobile

computing and mobile networks, there is an increasing

concern about a sustainable vertical handoff mechanism for

large scale heterogeneous networks. In existing

communication technology, different types of networking

protocols often pose a challenge in rendering an effective

communication when the mobile user moves from one to

other forms of wireless networks (3G, 4G, WiMax, GPRS,

CDMA, WLAN, etc). One of the significant factors to ensure

an effective handoff mechanism is ensure a faster

authentication process handling all the complexities of

heterogeneous network. Hence, this paper discusses about the

significant research attempts being done to enhance the

vertical handoff performance with respect to handling

complexities of heterogeneity, ensuring faster authentication

process. The paper also discusses the existing literatures

towards study of WLAN and CDMA network and finally the

paper discusses about the significant research gaps identified

by in-depth analysis of the outcomes of the existing

literatures.

Keywords

Handoff, vertical handoff, heterogeneous network, WLAN-3G

1. INTRODUCTION With the increasing demands of the pervasiveness and data

availability, there has been a lot of revolution changes in the

cellular communication technology witnessed most recently.

As cellular system offers infrastructure-dependent

connectivity, it is very important that there should be seamless

connectivity among the existing mobile user [1]. At present,

there are various types of communication technologies e.g.

UMTS, GPRS, 2G, 3G, 4G, WLAN, WiMax, CDMA etc. All

these networking technologies differ from each other in their

respective protocol stacks [2]. Owing to such differences in

the communication protocols, it leads to various problems e.g.

i) increased capacity for connecting new calls, ii) change of

user behavior, iii) channel interference, iv) unanticipated call

termination, v) outage etc. Therefore, in order to avoid all

these mentioned problems, it is essential that handoff

mechanism be performed for controlling such networking and

connectivity pitfalls. An efficient handoff mechanism leads to

enhanced reception with less probability of call drop and also

design and implementation of precise handoff mechanism will

lead to better load-balancing algorithm for properly managing

the multiple resources in the cellular network [3][4][5]. Such

principles of handoff mechanism is also strengthened by

incorporating handoff prioritization techniques [6][7]. The

existing handoff algorithm always attempts to minimize the

frequency of handoff event, which is quite detrimental for

optimal communication performance in large traffic situation.

Hence, handoff prioritization can be done using guard channel

method and queuing method [8]. The first technique reserves

a constant or changing number of channels required for

handoff, while the second technique is used for balancing the

load.

In existing system, there are 4 types of standard protocols that

is used for performing handoff mechanism viz. i) Mobile-

assisted handoff [9], ii) Network-controlled handoff [10], iii)

Soft and hard handoff [11], and iv) Mobile-Controlled

handoff [12]. Essentially, the handoff scheme has been also

reviewed with respect to 5 different schemes e.g. i) priority

scheme, i) handoff calls, iii) non-priority scheme, iv) queuing

scheme, and v) handoff call queuing scheme [13]. With the

upcoming technological requirements in 4G, Internet-of-

Things, Cloud Computing etc, it is important that handoff

mechanism be thoroughly investigated. Our prior work [14] a

Survey on Delay in Vertical Handoff in Heterogeneous

Wireless Networks has reviewed mainly the delay factor in

vertical handoff by discussing the work towards probe delay,

authentication delay, decision delay, re-association delay. The

paper also discussed certain open issues; however, authors

strongly felt that there is a need to put forward some more

updated work in this regards. Hence investigations are

continued to find that there are also some significant studies

towards heterogeneity factor, authentication factor, and

WLAN-CDMA network. The paper [14] lacks the scope of

discussion of research gap in descriptive manner as well as in-

depth analysis of the existing research contribution. Hence,

this paper fulfills this need by performing an in-depth review

of literature towards the existing techniques of vertical

handoff mechanism and also significantly discusses about the

research gap being explored from the study. Section 2

discusses about the brief fundamentals of handoff and

highlights the technical requirements for carrying out vertical

handoff schemes. Section 3 discusses about the most

significant literatures focusing on enhancing the performance

of heterogeneous network when vertical handoff takes place.

Section 4 discusses about the studies being considering the

authentication mechanism involved in vertical handoff

process. Section 5 discusses about the significant attempts of

researchers exclusively towards WLAN and CDMA. Finally

Section 6 highlights the research gap identified after in-depth

analysis of the literatures and Section 7 summarizes the

manuscript.

2. STUDIES TOWARDS HANDOFF The handoff can be said to be performed when a user gets the

connectivity of their data even when they are moving from

one to different networking area [15]. In telecommunications

handoff might be conducted due to different reasons:

When the Mobile station moves away from one cell to

another,

When a new call is originating from a Mobile station

belonging to a cell, whose new calls connecting capacity




36

is used up. Then this call is transferred to the cell which

is overlapped on this.

When the same channel is accessed by the two Mobile

stations belonging to different cells then the channel gets

interfered, the call is transferred to a different channel in

the same cell or different channel in another cell in order

to avoid the interference.

When received signal level values and received signal

quality values are low on the serving cell and better on

the neighbor cell; etc.

Generally, handoff is of two types i) horizontal handoff and ii)

vertical handoff [15]. A horizontal handoff occurs between

two network access points that use the same network

technology and interface. A vertical handoff is a mechanism

to perform handoff operation between the two different types

of network access point by deploying different networking

technologies [16]. The schema of horizontal and vertical

handoff is shown in Fig.1

3PR3

WLAN-1

WLAN-2

Horizontal

Handoff Vertical

Handoff

Fig 1: Schema of Vertical handoff

Majority of the method adopted to perform handoff are

categorized to hard and soft handoff [15].

Before, starting to review the existing literatures on vertical

handoff mechanism it is important to understand the factors to

be considered for implementing a handoff mechanism over

the heterogeneous network, which are as follows:

There should be a reduced number of handoff events as

more number of handoff events often results in

degradation of quality of signal with maximized

probability of packet dropping factor, also results in

additional load on the traffic; hence, it should be kept as

low as possible.

The handoff should be accomplished in the shortest

duration of time (low delay).

The handoff mechanism should offer reliable and secure

data transmission with seamless connectivity over

heterogeneous networks.

In case of heavy traffic on WLAN, it often results in data

overflow. Hence, performing handoff mechanism over

such WLAN traffic should be avoided etc.

3. STUDIES TOWARDS

HETEROGENEOUS NETWORK Heterogeneous network refers to wireless networks that are

using different access technologies. The type of handoff that

takes place in heterogeneous network is vertical handoff. At

present, the existing specifications (fixed IPv6) of the internet

protocol are found not to support vertical handoff. As IP in

existing internet protocol is the universal standard, hence, all

the entities beyond it will be abstracted from the

communication-based application. Hence, in order to support

IPv6, a background process is required to be designed and to

be executed in the network layer that performs switching

among the heterogeneous networking protocols. The

background process in the network is then used to select the

specific network depending on the speed of the active

networks, utility cost, Quality-of-Service etc. However, such

selection of the network is highly customizable as well as

necessary changes in the protocol stack can be done based on

the application requirements. Once the network is selected,

the handoff mechanism encapsulates the IP datagram in the

precise versions of radio access operation to be used.

In case of vertical handoff mechanism, adoption of WLAN is

found to be very frequent. In the area of vertical handoff, it

was also found that decisions were formulated by comparing

the signal strength of the existing network with certain

significant benchmarked value, which is also called as

threshold. However, such techniques are not that complex and

are feasible to get it integrated with other attributes e.g.

channel capacity, cost etc in order to formulate better handoff

decision. Some of the techniques based on signal strength are

i) Adaptive lifetime based vertical handoff mechanism

presented by Zahran et al. [17], ii) adaptive threshold based

schemes presented by Mohanty [18], distance based

prediction techniques presented by Yan et al. [19]. It is

significant to consider these studies as signal strength, handoff

delay, and security are some of the significant network

parameters in study of vertical handoff mechanism. The

vertical handoff mechanism is ensured by performing i)

collection of handoff information, ii) decision for handoff, and

iii) execution of handoff. The effectiveness factor depends on

quantity of successful handoff with respect to cumulative

handoff being made. Table 1 highlights some of the

significant research attempts being made towards vertical

handoff in heterogeneous network.

Table.1: Summary of Studies on Vertical Handoff in Heterogeneous Network

Authors Handoff Problem Techniques Adopted Performance

Parameters

Inference

Choi and Cho

[20]

Next generation

network and its

Seamless mobility

Request processing for

mobile nodes by neighbor

nodes

Speed of mobile node,

handoff probability,

Dropped packets,

energy

faster handoff

Outcomes not benchmarked

Zahran et al.

[21]

3G cellular and

WLAN

Threshold scheme based

on signal threshold

Speed, no. of handoffs,

bandwidth, delay,

Enhances utilization of system

resources

http://en.wikipedia.org/wiki/Wireless_networks




37

Outcomes not benchmarked,

Algorithm complexity not

discussed.

Liu et al. [22] Decision problem hysteresis based

technique, dwelling-timer

based algorithms

Handoff triggering

location

Theoretically studied on GPRS

and Wi-Fi

Issues of ping-pong effect and

reduction of matching ratio not

discussed.

Navarro et al.

[23]

Decision problem Algorithm based on state

space, reward function,

and transition feasibility

Reward, switching cost,

no. of handoff, weight

factor

optimal decision for

heterogeneous network

less focus on authentication

delays.

Arun and

Moni [24]

QoS provision over

4G

Developed power

management techniques

Throughput, channel

occupancy

dynamic and self-adaptable

algorithm

Outcomes not benchmarked less

focus on authentication scheme.

Gondara and

Kadam [25]

Vertical handoff in

4G

Analyzed and studied

existing techniques

-N/A Discussion paper

No discussion of research gap

Sharna &

Murshed [26]

Decision problem Markov decision Bandwidth, no. of

handoff, switching cost,

weight, discount factor

Achieved higher bandwidth

less focus on authentication

delays

Bijwe & Dethe

[27]

RSS Discussed RSS based

vertical handoff

-N/A Discussion paper

No discussion of research gap.

Nithyanandan

& Parthiban

[28]

WLAN-WiMax-LTE Gateway relocation

process

Power, delay, SNR,

packets dropped,

velocity,

better coupling techniques

Outcomes not benchmarked,

probe-based delay not discussed.

Kadhim &

Abed [29]

WLAN & Cellular

network

Hybrid Algorithm No. of handoff, velocity, reduction in handoff

Algorithm complexity not

discussed less extensive discussion.

Kunarak [30] UMTS-

WLAN/WiMax

Neural network RSS, distance, velocity,

dropping probability,

call arrival rate, grade of

services

Flexible handoff policy

Authentication delay not

discussed.

Shen et al. [31] Selection of good

QoS network

Principle Component

Analysis

Time, principle

components

Enhances system performance

Authentication delay not

discussed, algorithm complexity

not analyzed.

4. STUDIES TOWARDS

AUTHENTICATION MECHANISM Providing seamless vertical handoff calls for faster

deployment of authentication process and it is quite important

that mobile terminals to be appended with multiple base

stations or the access points in heterogeneous networks.

However, it is not that easy. In order to ensure the availability

of the services to mobile terminal, it is equally important to

conglomerate an efficient security standards, services offered

by service providers, and operators. Apart from security based

authentication system in vertical handoff in heterogeneous

network, various forms of services should be interoperable for

providing an effective mobility trait with existing wireless

standards. In the case of 3G, the authentication purely

depends on updating process of routing area. In case of 3GPP,

the authentication process depends on the key agreement and

cryptographic techniques. In case of WLAN, the

authentication process is again different. WLAN uses an

Extensible Authentication Protocol with Tunneled Transport

Layer security. Literatures have also found that probing phase

and re-association phase are the prime factors responsible

behind authentication delay in WLAN. Wherever a vertical

handoff takes place, for the purpose of security, an

authentication process should be performed to verify the

identity of the mobile terminal. In the wireless services,

secure and secret communication is desirable. If the

authentication is successful, then the encryption of data and

signaling is targeted. However, such types of existing

authentication schemes are associated with the pitfalls




38

pertaining to the mobility. Such authentication schemes are

found to consume considerable processing time as well as

mechanism of authentication is not found much efficient

owing to the frequent round trip as needed from one terminal

of service provider to the consumer’s domain. Therefore,

there is a need of fast as well as efficient authentication policy

that uses authentication server located near the mobile

customer. Table 2 highlights summary of studies on Fast

Authentication Protocols in Vertical Handoff.

Table 2: Summary of Studies on Fast Authentication Protocols in Vertical Handoff

Authors Techniques Adopted Performance

Parameters

Accomplishment Limitation

Huang et al.

[32]

3G-WLAN-

cryptographic key

management

Delay, time, overhead of

key distribution

10 seconds of delay

accomplished

Key management could be

further enhanced; resource access

controls have more scope to be

upgraded.

Dutta et al.

[33]

Framework for

Handoff optimization

Mobility rate, packet loss,

jitter, buffering period

Reduces delay of

inter-domain handoff

Algorithm complexity is not

discussed.

Murtaza &

Ahmed [34]

3G-WLAN-adaptive

and predictive

scheme of network

selection

Latency, interference,

velocity, bandwidth,

packet error rate, energy

Ensures reduced

latency and zero loss of

packet

less consideration of energy of

mobile nodes.

Zahran and

Sreenan [35]

Broker-based schema

for heterogeneous

network

Delay, interruption,

probability,

energy saving,

resource management,

proactive handoff,

reduced delay

Authentication is less secured.

Faisal & Khan

[36]

Reactive and

proactive Scheme

Delay A simple technique to

reduce delay

Address acquisition problems not

discussed, outcomes not discussed

extensively.

Wanalertlak et

al. [37]

Global path cache Delay, prediction of next

AP, no. of cache

Reduced time to find

AP

Authentication delay less

emphasized, problem of MAC

contention not considered.

Khan [38] Localized re-

authentication

technique

Authentication latency Enhanced performance

of authentication

Less evidences of outcomes and

data analysis.

Priya et al.

[39]

Elgamal based

authentication

Throughput Resistive against DoS

attack

Improvement of authentication

delay not discussed.

Idrissi et al.

[40]

3G-WLAN Bandwidth, signaling

cost, authentication delay

Highly resistance

against replay attack

Not applicable for dense

network.

Moon [41] 3G-WLAN-IMS

registration method

Delay, arrival rate Enhanced SIP Outcomes not benchmarked.

5. STUDIES ON WLAN AND CDMA Most recently, there has been increasing attention towards

understanding the viability of performing an efficient handoff

mechanism for WLAN and CDMA cellular network. In this

regards, it should be known that the principle of handoff only

occurs during the cases of i) mobile upwards, ii) mobile

downwards, and iii) mobile through. Mobile upwards takes

place when the mobile host moves from CDMA network

(outside of WLAN) to WLAN network. Mobile download

takes place when the mobile host moves from WLAN to other

network that is connected to CDMA network. Mobile through

takes place when any one of the available network is selected

for media selection layer. Performing handoff mechanism for

the CDMA networks as well as WLAN is never an easy task

owing to their differences in the network entities. Usually,

WLAN is used for encapsulating the hotspot zones with

maximized data rate and minimized cost. The transmission

area of CDMA is quite bigger than WLAN that offers network

connectivity in minimized data rate and maximized cost.

Hence, this is the significant tradeoff in WLAN and CDMA

network performance. Although previous sections have

highlighted some studies focusing on vertical handoff

mechanism, but the discussion was mainly carried out to

highlight vertical handoff effectiveness and not much on the

case studies on heterogeneity. Hence, we will look into some

of the studies performed till date on WLAN and CDMA.

The study conducted by Narisetti et al. [42] has presented a

design of a vertical handoff framework considering WLAN

and CDMA networks. The outcome of the study shows better

mobility management and significantly minimizes the delay

during vertical handoff. A similar type of the study was also

presented by Chou et al., that used intelligent agents for i)

load balancing and ii) authentication process. The study has

considered pre-authentication along with SIM based

validation mechanism for the UMTS users. The outcome of

the study was done considering i) blocking ratio, ii) packet

loss ratio, iii) proportion for new call blocking, iv) ratio of call

interruption, v) overhead on channel capacity. The outcome of

this study using intelligent agent was compared with

techniques without mobile agents and convention mobile




39

agent to find that it offers better performance. Kim et al. [44]

have presented an algorithm for selecting context-based

network that depends on distance data, signal strength, and

process of selection of network. The outcomes of the study

show better blocking probability, packet dropping probability,

and number of handoff. Agarwal and Kaur [45] have designed

an algorithm for vertical handoff for WLAN and CDMA. The

outcomes of the study were evaluated using throughput,

handoff delay and were not benchmarked. Similar pattern of

study was also carried out by Pande and Mhala [46]. The

simulation study was done in NS2 considering the

performance parameters as network delay, time, throughput.

However, the outcomes were not found to be benchmarked.

The next section will discuss about the significant research

gap that has been witnessed in the existing contribution

toward vertical handoff mechanism.

6. RESEARCH GAP From the viewpoint of the existing studies towards vertical

handoff mechanism in heterogeneous network, it can be said

that all the existing studies have their potential merit point as

well as limitation. Table 1 and Table 2 highlights the

inference of the trends of the work being witnessed for

enhancing handoff performance exclusively taking the case

studies of heterogeneous network. The research gaps explored

in the existing studies are as follows:

6.1 Less Emphasis to System Requirements Studies considering WLAN and 3G cellular services usually

consider to hide the authentication delay using cellular

services. A good example to understand this is if the WLAN

network is encapsulated by the 3G network while a mobile

terminal performs handoff from 3G to Wi-Fi, it is seen that

mobile terminal has the capability to retain the 3G connection

until the authentication process of Wi-Fi is accomplished.

However, these sorts of approach are accompanied with

pitfalls. The first pitfall is that such techniques cannot ensure

the availability of WLAN to be always covered in 3G

network. Second pitfall factor is, such techniques are less

applicable to WLAN as it supports multiple Access Stations.

Hence, seamless authentication delay is major problem in

WLAN and 3G cellular network, as owing to multiple AS,

authentication delay is more.

6.2 Less efficient mechanism of problem

formulation Majority of the existing studies towards heterogeneous

networks and its associated handoff mechanism are

formulated considering large number of machines (or

computing devices) and network parameters. From algorithm

implementation viewpoint, such consideration of large

number of research variable will significantly affect the

algorithm performance. Hence, there is a need to evolve up

with a design tactics that can formulate a precise parameter

for performing decision operation of performing handoff

mechanism.

6.3 Improper Algorithm Consideration It was also seen that certain algorithms were designed using

evolutionary techniques like neural network. Adoption of

such techniques is good enough for offline analysis but never

for online analysis. Training algorithm offers preciseness only

with the availability of data, which cannot be ensured in

online case studies of handoff mechanism.

6.4 Less Emphasis on Authentication

factor In majority of the existing studies, the term authentication is

found to posses dual meaning, where both the meanings are

quite valid viz. authentication using networking protocol

during handoff and authentication using security protocols

during handoff mechanism. Interesting, all the studies are

significantly found to ignore the significance of security or

cryptographic implementation for contributing fast

authentication standards. Less work is done towards

implementing new and robust cryptographic standards over

heterogeneous network to ensure a fail-proof authentication

system. Although there are certain studies using

cryptographic technique, but those studies were found not to

discuss about the effectiveness of the cryptographic

techniques to reduce authentication delays in large scale

handoff system with variables like mobility of the users.

6.5 Less Benchmarked Studies Majority of the existing studies towards vertical handoff

mechanism were discussed in the research papers. However,

very few benchmarked outcomes were observed. Although

some of the studies have explicitly claimed that their

outcomes were better but there is no mean to prove it with

respect to other existing studies.

6.6 Less Improvement in WLAN-CDMA The studies towards WLAN and CDMA are witnessed with

positive outcomes as there are less number of switches

between CDMA and WLAN network. Although, such

outcomes are in compliance with real-time requirement, it

seriously posses limitations. Imprecise selection of research

variables in such studies will lead to unwise resource

consumption that will directly affect the performance of the

networking devices which is incorporated with such

algorithms.

7. CONCLUSION Repeated discussion of theory is avoided in this manuscript as

in existing system there is availability of various research

paper highlighting the same over internet. The prime attempt

made in this paper is to highlight some of the significant

studies undertaken in vertical handoff schemes in

heterogeneous wireless network and extract research gap.

Hence, it can be seen from the paper that there is a need of

performing investigation towards designing an effective

authentication protocol. This paper identified the issues

mainly in WLAN-CDMA; future work will be in similar

direction. The prime objective of future work will be to

evolve with an improved vertical handoff algorithm by

considering multiple challenging system and network

parameters in order to reduce decision delay. The future work

will also consider a mechanism to select the Access Point

based on distance, power consumption, cost and bandwidth by

reducing the delay on multiple test-scenarios of mobility.

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